Unwrapping tricky cylinder
I was in a similar situation recently. Most online advice was "select one quad and then use the Follow Active Quads thingy", but that wasn't an option for my model.

What helped me was the Cylinder Projection unwrap method, with Direction set to "Align to Object" and both the "Correct Aspect" and "Scale to Bounds" checkboxes checked:


If the holes in your model aren't important and don't actually need to be in your UV map, make sure to deselect them first.